Surface treatment of aluminum profile before electrostatic powder spraying and pure water washing process

Abstract

The present application belongs to the technical field of profile surface treatment, and particularly relates to a surface treatment and pure water washing process of aluminum profile before electrostatic powder spraying, which comprises degreasing, primary water washing, secondary water washing, passivation, circulating pure water washing and ultraviolet treatment. By adding a repairing agent, mercaptoethanol ester of cinnamic acid, and a promoter, cerium ammonium nitrate, into the passivation liquid, the repairing agent is oxidized to form a disulfide bond by the oxidation of the mercapto group, so as to increase the compactness of the film layer; the disulfide bond formed by the oxidation of the mercapto group in the mercaptoethanol ester of cinnamic acid constitutes a dynamic structure, so that the passivation film generated has a self-repairing effect; and since the benzene ring in the mercaptoethanol ester of cinnamic acid is a non-polar group, and the ester group is close to the non-polar group, the conductivity error of the surface of the aluminum profile is significantly reduced. The double bond in the cinnamic acid group in the passivation film on the surface of the aluminum profile is further polymerized by ultraviolet treatment, so as to enhance the network structure of the passivation film and improve the corrosion resistance.

Description

Technical Field

[0001] This invention relates to the field of profile surface treatment technology, specifically, to a surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating. Background Technology

[0002] With the development of the times and the popularization of environmental awareness, traditional spraying processes have poor processing capabilities for profiles and are inconsistent with modern environmental protection concepts. The emerging electrostatic powder coating process has greatly improved the problems of profile processing and environmental protection.

[0003] In powder coating, the coating performance is not only related to the characteristics of the powder coating, but also closely related to the coating process parameters and the surface treatment of the profile. If the profile surface is not effectively cleaned in the pretreatment process, it will directly affect the coating quality, leading to problems such as blistering, peeling, and uneven color. Therefore, it is necessary to further remove surface impurities through a pure water washing process, improve the cleanliness of the workpiece, reduce conductivity, and lay the foundation for high-quality coating.

[0004] In the application "CN201710278757.0" entitled "A Powder Coating Process for Aluminum Profiles", the profiles are not washed with water after chromium passivation. Although the waterless process can improve production efficiency, the profiles carry residual chemicals, resulting in poor electrostatic powder coating effect. In the application "CN201310101733.X" entitled "Polyester Powder Coating Process for Aluminum Alloy Profiles", the aluminum alloy profiles are washed with water three times, chromated, and then washed with water three times. The water washing process is not only cumbersome and consumes a lot of water, but also does not use pure water for cleaning, resulting in high electrical conductivity of the aluminum alloy profiles.

[0005] To improve the corrosion resistance of aluminum profiles, existing technologies typically employ chromium-free passivation. However, the resulting passivation film exhibits lower corrosion resistance than traditional hexavalent chromium passivation films and lacks sufficient self-healing ability, making scratches or cracks prone to causing corrosion. Furthermore, in actual aluminum profile surface conductivity testing, to improve testing efficiency and save time, it is inconvenient to test each aluminum profile individually. Instead, the conductivity of the pure water in the final cleaning tank during the circulating pure water wash is often directly tested. However, this method yields a significant error compared to the surface conductivity of the aluminum profile after pure water washing, with an error of approximately 5 μs / cm. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention proposes a surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating, which improves the corrosion resistance and self-healing properties of the profiles, enhances the surface cleanliness, and reduces the surface conductivity error, thus laying the foundation for high-quality electrostatic powder coating.

[0007] A surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating includes the following steps:

[0008] S1, degreasing

[0009] The aluminum profile surface is sandblasted, and then pre-degreased by spraying the surface with diluted acidic degreaser to remove surface oil. Next, the surface of the aluminum profile is sprayed with diluted acidic degreaser for main degreasing to further remove stubborn oil. After the main degreasing is completed, the aluminum profile enters the water washing stage to avoid residual acid affecting subsequent processes.

[0010] Preferably, the temperature of the pre-degreasing treatment stage is 50–60°C, the spray pressure is controlled at 0.1–0.2 MPa, and the spray volume is 8–12 L / (m³). 2 (min), the pre-degreasing time should be adjusted according to the degree of contamination of the profile, and the time should be controlled between 3 and 8 minutes.

[0011] Preferably, the temperature of the main degreasing stage is 50–60°C, the spray pressure is controlled at 0.2–0.3 MPa, and the spray volume is 15–20 L / (m³). 2 (min), the time is 3 to 5 minutes.

[0012] Preferably, the acidic degreasing agent is commercially available, and the percentages of each component are as follows: sulfuric acid 35-42 wt%, hydrofluoric acid 8-10 wt%, surfactant 4-6 wt%, metal chelating agent 4-6 wt%, and the remainder is water.

[0013] Preferably, the effective content of the sulfuric acid is 98%.

[0014] Preferably, in the diluted acidic degreasing agent solution, the mass ratio of acidic degreasing agent to water is 25:980-1020.

[0015] S2, Level 1 water washing

[0016] After primary degreasing, the aluminum profiles are rinsed with tap water or soaked for a first-stage water wash to remove residual degreasing agent from the surface of the aluminum profiles, ensuring that the residual acid concentration in the cleaning tank water is ≤1.0‰.

[0017] Preferably, the spraying pressure is controlled at 0.15–0.3 MPa, and the spraying rate is 10–15 L / (m³). 2 (min), the time is 1 to 2 minutes.

[0018] Preferably, the soaking time is 5 to 10 minutes.

[0019] S3, Secondary water washing:

[0020] The aluminum profiles after the first water wash are then subjected to a second water wash to further reduce the concentration of surface contaminants.

[0021] Preferably, the secondary water washing adopts a counter-current rinsing design, with the water flow rate controlled at 3-5 L / (m³). 2 (·min), water washing time 0.5~1min, ensuring residual acid concentration in the cleaning tank water ≤0.5‰.

[0022] The core of the countercurrent rinsing is that the water flows in the opposite direction to the aluminum profile's running direction. Water is injected from the end of the secondary water washing tank (aluminum profile outlet side), flows to the front end of the secondary water washing tank (profile inlet side), and finally flows back from the front end to the primary water washing tank to replenish the water used in the primary water washing.

[0023] S4, passivation

[0024] Adjust the pH of the passivation solution to 2.8–3.5, and then immerse the aluminum profile after secondary water washing into the pH-adjusted passivation solution for passivation treatment.

[0025] Preferably, the percentages of each component in the passivation solution are as follows: hydrofluoric acid 2-4 wt%, oxalic acid 1-3 wt%, fluorozirconic acid 3-5 wt%, film-forming aid 0.1-0.3 wt%, polyacrylic acid 0.5-0.7 wt%, polyethylene glycol 0.2-0.4 wt%, chelating agent 1.5-2.5 wt%, accelerator 0.4-0.8 wt%, repair agent 0.5-0.7 wt%, dispersant 0.1-0.2 wt%, and the remainder is water.

[0026] Preferably, the chelating agent is one or more of aminotrimethylenephosphonic acid, disodium ethylenediaminetetraacetate, pentasodium aminotrimethylenephosphonate, and ethylenediaminetetramethylenephosphonic acid.

[0027] Preferably, the film-forming aid is one or more of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane.

[0028] Preferably, the accelerator is cerium ammonium nitrate and the dispersant is OP-10 emulsifier.

[0029] Preferably, the preparation method of the repair agent is as follows: cinnamic acid, 2-mercaptoethanol, catalyst, and anhydrous toluene are added to an esterification reactor and heated to reflux at 90-110°C under nitrogen protection. During the reaction, the generated water is removed, and the esterification reaction is considered to be complete when no more water is generated. The product is cinnamic acid mercaptoethanol ester. The product is washed with saturated sodium bicarbonate solution until neutral and dehydrated under vacuum to obtain the repair agent.

[0030] Preferably, the molar ratio of cinnamic acid to 2-mercaptoethanol is 1:1 to 1.2.

[0031] Preferably, the catalyst is p-toluenesulfonic acid, and the amount added is 0.8 to 1.1% of the mass of cinnamic acid.

[0032] Preferably, the volume ratio of 2-mercaptoethanol to anhydrous toluene is 1:5 to 6.

[0033] Preferably, the passivation treatment is performed at a temperature of 25–30°C for 3–5 minutes.

[0034] The roles of the components in the passivation solution are as follows: hydrofluoric acid is used to activate the surface of the aluminum profile; oxalic acid is used to complex Al. 3+ and Zr 4+ It slows down the film formation rate, making the film formation more uniform; fluorozirconic acid is the main film-forming agent; silane coupling agent is the film-forming aid, which improves the adhesion of the passivation film by forming Si-O-Al bonds; polyacrylic acid is used to fill the micropores of the passivation film layer, and the carboxyl groups react with Al... 3+ and Zr 4+ Coordination enhances the interaction between the agent and the substrate; chelating agents prevent passivation solution precipitation; cerium ammonium nitrate, the accelerator, not only accelerates film formation and optimizes the film structure, but also allows the thiol groups in the repair agent cinnamic acid mercaptoethanol ester to be preferentially oxidized to form disulfide bonds, increasing the film density. The disulfide bonds formed by the oxidation of thiol groups in cinnamic acid mercaptoethanol ester constitute a dynamic structure, giving the passivation film a self-repairing effect; the passivation time is relatively short, and the double bond reactivity in cinnamic acid mercaptoethanol ester is lower than that of thiol groups, so the double bonds in cinnamic acid mercaptoethanol ester are basically preserved, and further polymerization is carried out after UV treatment; the addition of polyethylene glycol provides flexible segments, providing a basis for repair and filling.

[0035] S5, Circulating pure water washing

[0036] The passivated aluminum profiles were washed with pure water by immersion or spraying to remove metal ions and tiny particles. After draining, the surface conductivity was measured.

[0037] Preferably, the conductivity of the pure water is ≤50μS / cm.

[0038] Preferably, the spray system uses multi-stage series cleaning tanks. Through counter-current recycling technology, the purified water used for the rinsing process is re-entered into the purified water tank for reuse. To ensure the conductivity of the purified water in the tank is ≤50μS / cm, it can be maintained by periodically draining old water and replenishing it with fresh purified water. The series cleaning tanks are designed with four stages to ensure cleaning quality. The conductivity and pH value of the water in both the purified water tank and the cleaning tank are monitored hourly. The pH of the purified water in the tank is controlled between 6.8 and 8.0 to avoid excessive acidity or alkalinity affecting coating adhesion; the pH value can be adjusted by adding sodium bicarbonate solution.

[0039] Preferably, the spraying pressure is controlled at 0.5–1 MPa, and the spraying rate is 10–15 L / (m³). 2(min), the time is 1 to 2 minutes.

[0040] Preferably, the soaking time is 1 to 3 minutes and the temperature is 20 to 30°C.

[0041] Preferably, the cleaning tank is made of 304 stainless steel or PP material, with a smooth inner wall without dead corners to avoid residual dirt, and is equipped with a heating coil and a circulating filtration system.

[0042] Preferably, the spacing and angle of the spray nozzles are adjustable to ensure that the spray coverage has no blind spots, and the high-pressure spray removes impurities from deep holes or gaps.

[0043] Preferably, the pure water is provided by a pure water preparation system, the preparation process of which includes pretreatment and fine treatment.

[0044] Furthermore, the pretreatment involves removing suspended solids and organic matter from tap water through sand filtration and activated carbon filtration, and then removing more than 90% of dissolved salts through an RO membrane; the fine treatment employs mixed-bed ion exchange resin or electro-deionization technology.

[0045] After the aluminum profiles are drained following a cycle of pure water washing, a residual water film remains on their surface. The measured conductivity value is actually the conductivity of the pure water within this residual film. The thinner the residual water film, the closer the conductivity of the aluminum profiles after the cycle of pure water washing is to that of pure water, resulting in a smaller deviation and better production control. Because the benzene ring in the cinnamic acid mercaptoethanol ester in the passivation film is a nonpolar group, and the ester group is nearly nonpolar, the amount of residual water film on the surface of the aluminum profiles after subsequent cycles of pure water washing is significantly reduced. This results in a smaller conductivity deviation between the residual water film and the pure water after the cycle of washing, allowing for direct measurement of the conductivity of the pure water after the cycle of washing, saving testing time.

[0046] S6, UV treatment

[0047] The aluminum profile is dried after being washed with circulating pure water and then subjected to ultraviolet treatment to obtain a surface-treated aluminum profile.

[0048] Preferably, the drying temperature is 70-80°C and the drying time is 30-40 minutes.

[0049] Preferably, the ultraviolet treatment temperature is 50–60°C and the light intensity is 30–40 mW / cm². 2 The wavelength is 365nm and the time is 20-30min.

[0050] The cinnamic acid groups in the passivation film on the surface of aluminum profiles contain double bonds. Through ultraviolet treatment, the double bonds are further polymerized, which enhances the network structure of the passivation film.

[0051] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows:

[0052] 1. The aluminum profile obtained by the surface treatment and pure water washing process provided by the present invention has an electrical conductivity of 20-30 μS / cm, while the electrical conductivity of the aluminum profile surface after treatment by the prior art is usually around 50 μS / cm. The appropriate decrease in electrical conductivity makes the subsequent electrostatic powder coating effect better.

[0053] 2. The passivation film on the surface of the aluminum profile of the present invention has strong adhesion, and the adhesion is grade 0 in the cross-cut adhesion test (measured according to GB / T9286-2021).

[0054] 3. The passivation film on the surface of the aluminum profile of the present invention has excellent self-healing ability, which can effectively repair local scratches or cracks and other damage to the passivation film, and improve the protective effect of the passivation film on the aluminum profile.

[0055] 4. The passivation film structure on the surface of the aluminum profile of the present invention is dense, which further improves the corrosion resistance of the aluminum profile.

[0056] 5. The aluminum profiles obtained by using the surface treatment and pure water washing process provided by this invention have controllable electrical conductivity, are easier to test, have smaller errors, and are more conducive to quality control. Detailed Implementation

[0057] To further illustrate the technical means and effects of the present invention in achieving the intended purpose, the following detailed description of the specific implementation methods, structures, features and effects of the present invention, in conjunction with preferred embodiments, is provided below.

[0058] Example 1: A surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating, comprising the following steps:

[0059] S1, degreasing

[0060] The aluminum profile surface is sandblasted, and then pre-degreased by spraying the surface with diluted acidic degreaser to remove surface oil. Next, the surface of the aluminum profile is sprayed with diluted acidic degreaser for main degreasing to further remove stubborn oil. After the main degreasing is completed, the aluminum profile enters the water washing stage to avoid residual acid affecting subsequent processes.

[0061] The temperature during the pre-degreasing treatment stage is 55℃, the spray pressure is controlled at 0.15MPa, and the spray volume is 10L / (m³). 2 (min), the time is 5min.

[0062] The temperature of the main degreasing stage is 55℃, the spray pressure is controlled at 0.25MPa, and the spray volume is 17L / (m³). 2 (min), the time is 4min.

[0063] The acidic degreasing agent is commercially available, and the percentages of each component are as follows: sulfuric acid 40 wt%, hydrofluoric acid 10 wt%, sodium dodecyl sulfate surfactant 5 wt%, aminotrimethylene phosphonic acid metal chelating agent 5 wt%, and the remainder is water.

[0064] The effective content of the sulfuric acid is 98%.

[0065] In the diluted acidic degreasing agent solution, the mass ratio of acidic degreasing agent to water is 25:1000.

[0066] S2, Level 1 water washing

[0067] After primary degreasing, the aluminum profiles are rinsed with tap water to remove residual degreasing agent from the surface until the residual acid concentration in the rinsing tank is 0.8‰.

[0068] The spray pressure is controlled at 0.25 MPa, and the spray rate is 12 L / (m³). 2 (·min), the time is 1.5min.

[0069] S3, Secondary water washing:

[0070] The aluminum profiles after the first water wash are then subjected to a second water wash to further reduce the concentration of surface contaminants.

[0071] The secondary water wash adopts a counter-current rinsing design, with the water flow rate controlled at 4L / (m³). 2 (·min), washing time 0.8min, until the residual acid concentration in the washing tank water is 0.4‰.

[0072] The core of the countercurrent rinsing is that the water flows in the opposite direction to the aluminum profile's running direction. Water is injected from the end of the secondary water washing tank (aluminum profile outlet side), flows to the front end of the secondary water washing tank (profile inlet side), and finally flows back from the front end to the primary water washing tank to replenish the water used in the primary water washing.

[0073] S4, passivation

[0074] Adjust the pH of the passivation solution to 3, and then immerse the aluminum profile after secondary water washing into the passivation solution after adjusting the pH for passivation treatment.

[0075] The percentages of each component in the passivation solution are as follows: hydrofluoric acid 3 wt%, oxalic acid 2 wt%, fluorozirconic acid 4 wt%, film-forming aid 0.2 wt%, polyacrylic acid 0.6 wt%, polyethylene glycol 0.3 wt%, chelating agent 2 wt%, accelerator 0.7 wt%, repair agent 0.7 wt%, dispersant 0.15 wt%, and the remainder is water.

[0076] The chelating agent is aminotrimethylenephosphonic acid, the film-forming aid is γ-aminopropyltriethoxysilane, the accelerator is cerium ammonium nitrate, and the dispersant is OP-10 emulsifier.

[0077] The polyacrylic acid has a molecular weight of 2000, and the polyethylene glycol has a molecular weight of 600.

[0078] The preparation method of the repair agent is as follows: cinnamic acid, 2-mercaptoethanol, catalyst, and anhydrous toluene are added to an esterification reactor and heated to reflux at 100°C under nitrogen protection. During the reaction, the generated water is removed, and the esterification reaction is considered to be completed when no more water is generated. The product is cinnamic acid mercaptoethanol ester. The product is washed with saturated sodium bicarbonate solution until neutral and dehydrated under vacuum to obtain the repair agent.

[0079] The molar ratio of cinnamic acid to 2-mercaptoethanol is 1:1.1.

[0080] The catalyst is p-toluenesulfonic acid, and the amount added is 1% of the mass of cinnamic acid.

[0081] The volume ratio of 2-mercaptoethanol to anhydrous toluene is 1:5.5.

[0082] The passivation treatment was performed at a temperature of 28°C for 4 minutes.

[0083] S5, Circulating pure water washing

[0084] The passivated aluminum profiles were washed with pure water by spraying to remove metal ions and tiny particles. After draining, the surface conductivity was measured.

[0085] The conductivity of the pure water is 20 μS / cm.

[0086] The spray system is equipped with four-stage series cleaning tanks. Through countercurrent recycling technology, the pure water used for the pure water washing is recycled back into the pure water tank for reuse. The pH value of the pure water in the pure water tank is adjusted to 7.5 by adding sodium bicarbonate solution.

[0087] The spraying pressure is controlled at 0.7 MPa, and the spraying rate is 12 L / (m³). 2 (·min), the time is 1.5min.

[0088] The cleaning tank is made of 304 stainless steel with a smooth inner wall and no dead corners to avoid residual dirt. The tank is equipped with a heating coil and a circulating filtration system.

[0089] The nozzles of the spray system are spaced 20cm apart and angled at 45°.

[0090] The pure water is provided by a pure water preparation system, the preparation process of which includes pretreatment and fine treatment.

[0091] The pretreatment involves removing suspended solids and organic matter from tap water through sand filtration and activated carbon filtration, and then removing more than 90% of dissolved salts through an RO membrane; the fine treatment uses mixed-bed ion exchange resin technology.

[0092] S6, UV treatment

[0093] The aluminum profile is dried after being washed with circulating pure water and then subjected to ultraviolet treatment to obtain a surface-treated aluminum profile.

[0094] The drying temperature is 75°C and the time is 35 minutes.

[0095] The ultraviolet treatment temperature was 55℃, and the light intensity was 35mW / cm². 2 The wavelength was 365nm and the time was 25min.

[0096] Example 2: A surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating, comprising the following steps:

[0097] S1, degreasing

[0098] The aluminum profile surface is sandblasted, and then pre-degreased by spraying the surface with diluted acidic degreaser to remove surface oil. Next, the surface of the aluminum profile is sprayed with diluted acidic degreaser for main degreasing to further remove stubborn oil. After the main degreasing is completed, the aluminum profile enters the water washing stage to avoid residual acid affecting subsequent processes.

[0099] The temperature during the pre-degreasing treatment stage is 50℃, the spray pressure is controlled at 0.1MPa, and the spray volume is 12L / (m³). 2 (·min), the time is 8min.

[0100] The temperature of the main degreasing stage is 50℃, the spray pressure is controlled at 0.2MPa, and the spray volume is 20L / (m³). 2 (min), the time is 3 minutes.

[0101] The acidic degreasing agent is commercially available, and the percentages of each component are as follows: sulfuric acid 35 wt%, hydrofluoric acid 10 wt%, sodium dodecyl sulfate surfactant 4 wt%, aminotrimethylene phosphonic acid metal chelating agent 4 wt%, and the remainder is water.

[0102] The effective content of the sulfuric acid is 98%.

[0103] In the diluted acidic degreasing agent solution, the mass ratio of acidic degreasing agent to water is 25:980.

[0104] S2, Level 1 water washing

[0105] After primary degreasing, the aluminum profiles are rinsed with tap water to remove residual degreasing agent from the surface until the residual acid concentration in the rinsing tank is 0.8‰.

[0106] The spraying pressure is controlled at 0.15 MPa, and the spraying rate is 10 L / (m³). 2 (min), the time is 2 minutes.

[0107] S3, Secondary water washing:

[0108] The aluminum profiles after the first water wash are then subjected to a second water wash to further reduce the concentration of surface contaminants.

[0109] The secondary water wash adopts a counter-current rinsing design, with the water flow rate controlled at 3L / (m³). 2 (·min), washing time 1min, until the residual acid concentration in the washing tank water is 0.4‰.

[0110] The core of the countercurrent rinsing is that the water flows in the opposite direction to the aluminum profile's running direction. Water is injected from the end of the secondary water washing tank (aluminum profile outlet side), flows to the front end of the secondary water washing tank (profile inlet side), and finally flows back from the front end to the primary water washing tank to replenish the water used in the primary water washing.

[0111] S4, passivation

[0112] Adjust the pH of the passivation solution to 2.8, and then immerse the aluminum profile after secondary water washing into the passivation solution after adjusting the pH for passivation treatment.

[0113] The percentages of each component in the passivation solution are as follows: hydrofluoric acid 2 wt%, oxalic acid 3 wt%, fluorozirconic acid 3 wt%, film-forming aid 0.1 wt%, polyacrylic acid 0.5 wt%, polyethylene glycol 0.2 wt%, chelating agent 1.5 wt%, accelerator 0.4 wt%, repair agent 0.5 wt%, dispersant 0.1 wt%, and the remainder is water.

[0114] The chelating agent is aminotrimethylenephosphonic acid, the film-forming aid is γ-aminopropyltriethoxysilane, the accelerator is cerium ammonium nitrate, and the dispersant is OP-10 emulsifier.

[0115] The polyacrylic acid has a molecular weight of 2000, and the polyethylene glycol has a molecular weight of 600.

[0116] The preparation method of the repair agent is as follows: cinnamic acid, 2-mercaptoethanol, catalyst, and anhydrous toluene are added to an esterification reactor and heated to reflux at 90°C under nitrogen protection. During the reaction, the generated water is removed, and the esterification reaction is considered to be completed when no more water is generated. The product is cinnamic acid mercaptoethanol ester. The product is washed with saturated sodium bicarbonate solution until neutral and dehydrated under vacuum to obtain the repair agent.

[0117] The molar ratio of cinnamic acid to 2-mercaptoethanol is 1:1.

[0118] The catalyst is p-toluenesulfonic acid, and the amount added is 0.8% of the mass of cinnamic acid.

[0119] The volume ratio of 2-mercaptoethanol to anhydrous toluene is 1:5.

[0120] The passivation treatment was performed at a temperature of 25°C for 5 minutes.

[0121] S5, Circulating pure water washing

[0122] The passivated aluminum profiles were washed with pure water by spraying to remove metal ions and tiny particles. After draining, the surface conductivity was measured.

[0123] The conductivity of the pure water is 20 μS / cm.

[0124] The spray system is equipped with four-stage series cleaning tanks. Through countercurrent recycling technology, the pure water used for the pure water washing is recycled back into the pure water tank for reuse. The pH value of the pure water in the pure water tank is adjusted to 7.5 by adding sodium bicarbonate solution.

[0125] The spraying pressure is controlled at 0.5 MPa, and the spraying rate is 10 L / (m³). 2 (min), the time is 2 minutes.

[0126] The cleaning tank is made of 304 stainless steel with a smooth inner wall and no dead corners to avoid residual dirt. The tank is equipped with a heating coil and a circulating filtration system.

[0127] The nozzles of the spray system are spaced 20cm apart and angled at 45°.

[0128] The pure water is provided by a pure water preparation system, the preparation process of which includes pretreatment and fine treatment.

[0129] The pretreatment involves removing suspended solids and organic matter from tap water through sand filtration and activated carbon filtration, and then removing more than 90% of dissolved salts through an RO membrane; the fine treatment uses mixed-bed ion exchange resin technology.

[0130] S6, UV treatment

[0131] The aluminum profile is dried after being washed with circulating pure water and then subjected to ultraviolet treatment to obtain a surface-treated aluminum profile.

[0132] The drying temperature is 70°C and the time is 30 minutes.

[0133] The ultraviolet treatment temperature was 50℃, and the light intensity was 30mW / cm². 2The wavelength was 365nm and the time was 30min.

[0134] Example 3: A surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating, including the following steps:

[0135] S1, degreasing

[0136] The aluminum profile surface is sandblasted, and then pre-degreased by spraying the surface with diluted acidic degreaser to remove surface oil. Next, the surface of the aluminum profile is sprayed with diluted acidic degreaser for main degreasing to further remove stubborn oil. After the main degreasing is completed, the aluminum profile enters the water washing stage to avoid residual acid affecting subsequent processes.

[0137] The temperature during the pre-degreasing treatment stage is 60℃, the spray pressure is controlled at 0.2MPa, and the spray volume is 8L / (m³). 2 (min), the time is 3 minutes.

[0138] The temperature of the main degreasing stage is 60℃, the spray pressure is controlled at 0.3MPa, and the spray volume is 15L / (m³). 2 (min), the time is 5min.

[0139] The acidic degreasing agent is commercially available, and the percentages of each component are as follows: sulfuric acid 42 wt%, hydrofluoric acid 8 wt%, sodium dodecyl sulfate surfactant 6 wt%, aminotrimethylene phosphonic acid metal chelating agent 6 wt%, and the remainder is water.

[0140] The effective content of the sulfuric acid is 98%.

[0141] In the diluted acidic degreasing agent solution, the mass ratio of acidic degreasing agent to water is 25:1020.

[0142] S2, Level 1 water washing

[0143] After primary degreasing, the aluminum profiles are rinsed with tap water to remove residual degreasing agent from the surface until the residual acid concentration in the rinsing tank is 0.8‰.

[0144] The spraying pressure is controlled at 0.3 MPa, and the spraying rate is 15 L / (m³). 2 (·min), the time is 1min.

[0145] S3, Secondary water washing:

[0146] The aluminum profiles after the first water wash are then subjected to a second water wash to further reduce the concentration of surface contaminants.

[0147] The secondary water wash adopts a counter-current rinsing design, with the water flow rate controlled at 5L / (m³). 2(·min), washing time 0.5min, until the residual acid concentration in the washing tank water is 0.4‰.

[0148] The core of the countercurrent rinsing is that the water flows in the opposite direction to the aluminum profile's running direction. Water is injected from the end of the secondary water washing tank (aluminum profile outlet side), flows to the front end of the secondary water washing tank (profile inlet side), and finally flows back from the front end to the primary water washing tank to replenish the water used in the primary water washing.

[0149] S4, passivation

[0150] Adjust the pH of the passivation solution to 3.5, and then immerse the aluminum profile after secondary water washing into the passivation solution after adjusting the pH for passivation treatment.

[0151] The percentages of each component in the passivation solution are as follows: hydrofluoric acid 4 wt%, oxalic acid 1 wt%, fluorozirconic acid 5 wt%, film-forming aid 0.3 wt%, polyacrylic acid 0.7 wt%, polyethylene glycol 0.4 wt%, chelating agent 2.5 wt%, accelerator 0.8 wt%, repair agent 0.6 wt%, dispersant 0.2 wt%, and the remainder is water.

[0152] The chelating agent is aminotrimethylenephosphonic acid, the film-forming aid is γ-aminopropyltriethoxysilane, the accelerator is cerium ammonium nitrate, and the dispersant is OP-10 emulsifier.

[0153] The polyacrylic acid has a molecular weight of 2000, and the polyethylene glycol has a molecular weight of 600.

[0154] The preparation method of the repair agent is as follows: cinnamic acid, 2-mercaptoethanol, catalyst, and anhydrous toluene are added to an esterification reactor and heated to reflux at 110°C under nitrogen protection. During the reaction, the generated water is removed, and the esterification reaction is considered to be completed when no more water is generated. The product is cinnamic acid mercaptoethanol ester. The product is washed with saturated sodium bicarbonate solution until neutral and dehydrated under vacuum to obtain the repair agent.

[0155] The molar ratio of cinnamic acid to 2-mercaptoethanol is 1:1.2.

[0156] The catalyst is p-toluenesulfonic acid, and the amount added is 1.1% of the mass of cinnamic acid.

[0157] The volume ratio of 2-mercaptoethanol to anhydrous toluene is 1:6.

[0158] The passivation treatment was performed at a temperature of 30°C for 3 minutes.

[0159] S5, Circulating pure water washing

[0160] The passivated aluminum profiles were washed with pure water by spraying to remove metal ions and tiny particles. After draining, the surface conductivity was measured.

[0161] The conductivity of the pure water is 20 μS / cm.

[0162] The spray system is equipped with four-stage series cleaning tanks. Through countercurrent recycling technology, the pure water used for the pure water washing is recycled back into the pure water tank for reuse. The pH value of the pure water in the pure water tank is adjusted to 7.5 by adding sodium bicarbonate solution.

[0163] The spraying pressure is controlled at 1 MPa, and the spraying rate is 15 L / (m³). 2 (·min), the time is 1min.

[0164] The cleaning tank is made of 304 stainless steel with a smooth inner wall and no dead corners to avoid residual dirt. The tank is equipped with a heating coil and a circulating filtration system.

[0165] The nozzles of the spray system are spaced 20cm apart and angled at 45°.

[0166] The pure water is provided by a pure water preparation system, the preparation process of which includes pretreatment and fine treatment.

[0167] The pretreatment involves removing suspended solids and organic matter from tap water through sand filtration and activated carbon filtration, and then removing more than 90% of dissolved salts through an RO membrane; the fine treatment uses mixed-bed ion exchange resin technology.

[0168] S6, UV treatment

[0169] The aluminum profile is dried after being washed with circulating pure water and then subjected to ultraviolet treatment to obtain a surface-treated aluminum profile.

[0170] The drying temperature is 80℃ and the time is 40 minutes.

[0171] The ultraviolet treatment temperature was 60℃, and the light intensity was 40mW / cm². 2 The wavelength was 365nm and the time was 20min.

[0172] Comparative Example 1: A representative example 1 was selected, in which the repair agent in the passivation solution was removed, and all other aspects were the same as in Example 1, serving as Comparative Example 1.

[0173] Comparative Example 2: Example 1, which is representative, was selected. In step S6, no ultraviolet treatment was performed after drying. All other steps were the same as in Example 1. This was used as Comparative Example 2.

[0174] Comparative Example 3: A representative example, Example 1, was selected, and the accelerator cerium ammonium nitrate in the passivation solution was replaced with an equal amount of triethanolamine. All other aspects were the same as in Example 1. This was used as Comparative Example 3.

[0175] The conductivity of the pure water in the last cleaning tank after the circulating pure water washing step in Examples 1-3 and Comparative Examples 1-3 was 20 μS / cm.

[0176] The surface-treated aluminum profiles obtained in Examples 1-3 and Comparative Examples 1-3 were subjected to performance testing, as detailed in the table below.

[0177] Table 1

[0178]

[0179] Table 2

[0180]

[0181] The self-healing test method is as follows: The samples of Examples 1-3 and Comparative Examples 1-3 are scratched with a blade with a depth of 0.5 μm, a width of 3 μm, and a length of 1 cm. After being placed in an environment with a temperature of 80℃ and a humidity of 60% for 24 hours, the appearance changes are observed, and the corrosion resistance after repair is measured.

[0182] The corrosion resistance test was conducted according to the CASS test method in GB / T 10125-2021, with a test cycle of 24 hours. The corrosion resistance was reflected by calculating the weight loss rate.

[0183] As can be seen from Tables 1 and 2, in Comparative Example 1, without a repair agent, the number of non-polar groups in the passivation film is reduced, resulting in a large error between the surface conductivity of the aluminum profile and the conductivity of pure water. Due to the absence of a repair agent, the density of the passivation film decreases, the corrosion resistance decreases, surface scratches are difficult to repair, corrosive media spread rapidly, and the weight loss rate is higher after scratch treatment.

[0184] In Comparative Example 2, without UV treatment, the double bonds in the passivation film are difficult to polymerize, and the number of micropores in the film increases. This results in a higher error between the surface conductivity of the aluminum profile and the conductivity of pure water compared to Example 1, but better than Comparative Example 1. The corrosion resistance decreases, and the weight loss rate is slightly higher. The scratch repair effect is better after self-repair, and the weight loss rate remains basically unchanged after self-repair.

[0185] Comparative Example 3 replaced the accelerator with triethanolamine, which only promoted film formation but had no oxidizing properties. The thiol groups in the repair agent were difficult to form disulfide bonds, and the subsequent UV treatment efficiency was low, resulting in a decrease in film density. This led to a higher error between the surface conductivity of the aluminum profile and the conductivity of pure water compared to Example 1, but better than Comparative Example 1. The weight loss rate was high, the repair ability was poor, and the scratches on the surface were difficult to repair. Therefore, the weight loss rate also increased after self-repair.

[0186] In summary, it can be seen that aluminum profiles surface-treated using the methods of Examples 1-3 not only have smaller electrical conductivity errors, but also better corrosion resistance and self-healing ability.

[0187] Unless otherwise specified, all proportions and percentages mentioned in this invention are mass proportions and mass percentages; all raw materials are commercially available.

[0188] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating, characterized in that, The surface treatment and pure water washing process includes degreasing, primary water washing, secondary water washing, passivation, circulating pure water washing, and ultraviolet treatment; The passivation process involves adjusting the pH of the passivation solution to 2.8–3.5, and then immersing the aluminum profile after secondary water washing into the pH-adjusted passivation solution for passivation treatment. The percentages of each component in the passivation solution are as follows: hydrofluoric acid 2-4 wt%, oxalic acid 1-3 wt%, fluorozirconic acid 3-5 wt%, film-forming aid 0.1-0.3 wt%, polyacrylic acid 0.5-0.7 wt%, polyethylene glycol 0.2-0.4 wt%, chelating agent 1.5-2.5 wt%, accelerator 0.4-0.8 wt%, repair agent 0.5-0.7 wt%, dispersant 0.1-0.2 wt%, and the remainder is water; The chelating agent is one or more of the following: aminotrimethylenephosphonic acid, disodium ethylenediaminetetraacetate, pentasodium aminotrimethylenephosphonate, and ethylenediaminetetramethylenephosphonic acid. The film-forming aid is one or more of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; The accelerator is cerium ammonium nitrate, and the dispersant is OP-10 emulsifier; The preparation method of the repair agent is as follows: cinnamic acid, 2-mercaptoethanol, catalyst, and anhydrous toluene are added to an esterification reactor and heated to reflux at 90-110°C under nitrogen protection. During the reaction, the generated water is removed, and the esterification reaction is considered to be complete when no more water is generated. The product is cinnamic acid mercaptoethanol ester. The product is washed with saturated sodium bicarbonate solution until neutral and dehydrated under vacuum to obtain the repair agent. The ultraviolet treatment involves drying the surface of the aluminum profile after it has been washed with circulating pure water, and then performing ultraviolet treatment to obtain a surface-treated aluminum profile.

2. The surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating according to claim 1, characterized in that, The molar ratio of cinnamic acid to 2-mercaptoethanol is 1:1 to 1.2; The catalyst is p-toluenesulfonic acid, and the amount added is 0.8-1.1% of the mass of cinnamic acid. The volume ratio of 2-mercaptoethanol to anhydrous toluene is 1:5 to 6; The passivation treatment is performed at a temperature of 25–30°C for 3–5 minutes.

3. The surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating according to claim 1, characterized in that, The degreasing process involves sandblasting the surface of the aluminum profile, then spraying the surface of the aluminum profile with a diluted acidic degreasing agent for pre-degreasing treatment; followed by spraying the surface of the aluminum profile with a diluted acidic degreasing agent for main degreasing treatment, and finally, proceeding to the water washing stage after the main degreasing is completed.

4. The surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating according to claim 3, characterized in that, The temperature during the pre-degreasing treatment stage is 50–60℃, the spray pressure is controlled at 0.1–0.2 MPa, and the spray volume is 8–12 L / (m³). 2 (min), time is 3-8 minutes; The temperature of the main degreasing stage is 50–60℃, the spray pressure is controlled at 0.2–0.3 MPa, and the spray volume is 15–20 L / (m³). 2 (min), time is 3-5 minutes; In the diluted acidic degreasing agent solution, the mass ratio of acidic degreasing agent to water is 25:980-1020; the acidic degreasing agent is commercially available.

5. The surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating according to claim 1, characterized in that, The first-stage water washing involves spraying or immersing the aluminum profile after degreasing with tap water. The spraying pressure is controlled at 0.15–0.3 MPa, and the spraying rate is 10–15 L / (m³). 2 (min), the time is 1 to 2 minutes.

6. The surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating according to claim 1, characterized in that, The secondary water washing involves further reducing the concentration of surface contaminants by washing the aluminum profiles after the primary water washing. The secondary water wash adopts a counter-current rinsing design, with the water flow rate controlled at 3-5 L / (m³). 2 (·min), washing time 0.5~1min.

7. The surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating according to claim 1, characterized in that, The circulating pure water washing involves using pure water to immerse or spray the passivated aluminum profiles in circulating pure water. The conductivity of the pure water is ≤50μS / cm.

8. The surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating according to claim 7, characterized in that, The circulating pure water washing system is equipped with a multi-stage series cleaning tank. The spraying pressure is controlled at 0.5–1 MPa, and the spraying rate is 10–15 L / (m³). 2 (min), the time is 1 to 2 minutes.

9. The surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating according to claim 7, characterized in that, The pure water is provided by a pure water preparation system, the preparation process of which includes pretreatment and fine treatment; The pretreatment involves removing suspended solids and organic matter from tap water through sand filtration and activated carbon filtration, and then removing more than 90% of dissolved salts through an RO membrane; the fine treatment uses mixed-bed ion exchange resin or electro-deionization technology.

10. The surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating according to claim 1, characterized in that, The drying temperature is 70-80℃, and the time is 30-40 minutes; The ultraviolet treatment temperature is 50–60℃, and the light intensity is 30–40 mW / cm². 2 The wavelength is 365nm and the time is 20-30min.

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